Method and apparatus for determining a position of a gnss receiver

ABSTRACT

A method of determining a position of a GNSS receiver includes: receiving, at the GNSS receiver, information from at least two GNSS satellites and an estimated location area from a non-GNSS positioning application, determining candidate pseudoranges corresponding to candidate correlation peaks determined based on the information received from the at least two GNSS satellites; determining possible positions of the GNSS receiver using the candidate pseudoranges and the estimated location area; determining a best possible position of the GNSS receiver from the possible positions; and setting the best possible position as the position of the GNSS receiver; wherein when multiple candidate correlation peaks corresponding to one of the at least two GNSS satellites are determined, the estimated location area is usable to reduce the number of candidate correlation peaks prior to candidate pseudoranges being determined.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of International ApplicationNo. PCT/CA2011/001194, filed Oct. 26, 2011, which claims priority fromU.S. Provisional Application No. 61/406,921, filed Oct. 26, 2010, thecontents of which are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

The present application relates methods and apparatus for acquiringsatellites in a Global Navigation Satellite System (GNSS) and fixing aposition of a GNSS receiver.

BACKGROUND DISCUSSION

A Global Navigation Satellite System (GNSS) receiver requiresinformation from at least four GNSS satellites in order to determine itsthree dimensional position. The approximate distance between a GNSSsatellite and a receiver is generally referred to as a pseudorange. Thelocation of the GNSS satellites relative to the receiver has a majorimpact on the overall accuracy of the determined three dimensionalposition. In general, good satellite geometry occurs when satellites areevenly scattered relative to the receiver. When less than four GNSSsatellites are acquired or in a case of bad satellite geometry, astand-alone GNSS receiver may fail to fix its three-dimensionalposition. Difficulty in acquiring satellites is typically due to signaldegradation and unavailability of satellites in challenging environmentssuch as indoors, in densely forested areas or in deep urban locations,for example, where attenuation and multipath effects make it difficultfor the GNSS receiver to discriminate and acquire information from therequired number of GNSS satellites.

Other non-GNSS positioning techniques use several technologies such asWiFi and Cellular-based positioning, for example, which can provide asource of additional information to assist a stand-alone GNSS receiverwhen it cannot acquire a sufficient number of GNSS satellites or in thecase of bad satellite geometry. Cooperation between a GNSS receiver andany other positioning technology is referred to as Assisted-GNSS(A-GNSS). The assistance information generally includes ephemeris data(real or synthetic), timing data and/or position estimation.

A well known GNSS is the Global Positioning System (GPS). Inconventional Assisted-GPS (A-GPS) where initial position assistance isavailable, the initial position assistance may be used as an aid by thereceiver to allow the receiver to focus on signals from satellitespassing overhead. More generally, however, the initial positionassistance just provides a fallback position in case the GPS receiverstill fails to acquire information from a sufficient number ofsatellites or in case of bad satellite geometry. Such methods have beendescribed as hybrid positioning and generally involve an either/orselection between the outputs of two or more positioning technologiesincluding GPS, A-GPS, WiFi and Cellular-based positioning, for example.

SUMMARY

In an aspect of the present disclosure, there is provided, a method ofdetermining a position of a GNSS receiver including: receiving, at theGNSS receiver, information from at least two GNSS satellites; receiving,at the GNSS receiver, an estimated location area from a non-GNSSpositioning application; determining candidate pseudorangescorresponding to candidate correlation peaks determined based on theinformation received from the at least two GNSS satellites; determiningpossible positions of the GNSS receiver using the candidate pseudorangesand the estimated location area; determining a best possible position ofthe GNSS receiver from the possible positions; and setting the bestpossible position as the position of the GNSS receiver; wherein whenmultiple candidate correlation peaks corresponding to one of the atleast two GNSS satellites are determined, the estimated location area isusable to reduce the number of candidate correlation peaks prior tocandidate pseudoranges being determined.

In another aspect of the present disclosure, there is provided, a mobiledevice including: an antenna; a GNSS receiver for receiving informationfrom at least two GNSS satellites and for receiving an estimatedlocation area from a non-GNSS positioning application; and a processorin communication with the GNSS receiver; the processor determiningcandidate pseudoranges corresponding to candidate correlation peaksdetermined based on the information received from the at least two GNSSsatellites, determining a best possible position of the GNSS receiverfrom possible positions of the GNSS receiver determined using thecandidate pseudoranges and the estimated location area and setting thebest possible position as the position of the GNSS receiver; whereinwhen multiple candidate correlation peaks corresponding to one of the atleast two GNSS satellites are determined, the estimated location area isusable to reduce the number of candidate correlation peaks prior tocandidate pseudoranges being determined.

Collaboration methods between a GNSS receiver and non-GNSS positioningwith respect to the use of initial position assistance are described. Inthe methods and apparatus of the present embodiments, non-GNSStechnologies collaborate with a GNSS receiver and provide positioninginformation to facilitate fixing of a position of a GNSS receiver whenthe GNSS receiver is unable to fix its position independently.

Other aspects and features of the present embodiments will becomeapparent to those ordinarily skilled in the art upon review of thefollowing description of specific embodiments in conjunction with theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present application will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 is a schematic diagram of some components of a mobile deviceincluding a GPS receiver in communication with GPS satellites;

FIG. 2 is a block diagram of components of the mobile device of FIG. 1;

FIG. 3 is a block diagram of a GPS receiver in communication with GPSsatellites and a non-GNSS positioning application;

FIG. 4 is a block diagram depicting operation of a GPS receiveraccording to an embodiment;

FIG. 5 is a flow diagram depicting processing of correlation peaks;

FIG. 6 is a flow diagram depicting operation of a satellite acquisitionapplication;

FIG. 7 is a schematic diagram showing possible positions of a GPSreceiver as determined using the satellite acquisition application;

FIG. 8 is a flow diagram depicting a method of determining a position ofa GPS receiver using assisted positioning information from a non-GNSSpositioning application;

FIG. 9A is a schematic diagram showing two possible positions of a GPSreceiver when information from two GPS satellites is received;

FIG. 9B is a schematic diagram showing possible positions of a GPSreceiver determined using the method of FIG. 8;

FIG. 9C is a schematic diagram showing possible positions of a GPSreceiver as determined using a hybrid positioning system of the priorart;

FIG. 10 is a schematic diagram depicting operating of a GPS receiverusing a satellite acquisition application and a position determiningapplication according to an embodiment;

FIG. 11 is a schematic diagram showing possible positions of a GPSreceiver using a satellite acquisition application and a positiondetermining application according to an embodiment; and

FIG. 12 is a flowchart depicting collaboration between the GPS receiver,satellite acquisition application, position determining application andposition assisted-GPS application.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where considered appropriate, reference numerals may be repeated amongthe figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein may be practiced without these specificdetails. In other instances, well-known methods, procedures andcomponents have not been described in detail so as not to obscure theembodiments described herein. Also, the description is not to beconsidered as limiting the scope of the embodiments described herein.

It will be appreciated by a person skilled in the art that GPS isreferred to throughout the present application by way of example only.The methods and apparatus of the present application are applicable toany GNSS.

Referring to FIG. 1, a mobile device 10 receives information from GPSsatellites in order to determine its position. The mobile device 10 maybe a cell phone, a personal digital assistant, a Smartphone, an assettracking device, a tablet or laptop computer, a navigation device oranother device that is capable of determining its position with the helpof a non-GNSS positioning application. In the embodiments describedherein, assisted position information derived from a non-GNSSpositioning application includes at least initial, or coarse, positionassistance, which helps the GPS receiver 14 locate the GPS satellitespassing overhead more quickly than a stand-alone GPS receiver, forexample. The assisted position information derived from a non-GNSSpositioning application may be available locally, on the mobile device10, may be available through direct communication with a computer or maybe available via wireless communication with a server or database.

As shown in FIG. 2, the mobile device 10 includes an antenna 12 forreceiving wireless signals, a GPS receiver 14 in communication with theantenna 12, a processor 16 in communication with the antenna 12 and thereceiver 14. The mobile device 10 further includes a memory 18 thatcommunicates with the processor 16. The mobile device 10 may communicatewith a computer to receive an estimated location area from a non-GNSSpositioning application via a cellular data network, such as GPRS, EDGE,3G, 4G, WLAN, 762.11 g, or 762.11n, for example. The mobile device 10may further be capable of short range communication using Bluetooth™,for example. In one embodiment, the mobile device 10 includes an antenna12 and some GPS receiver components. For example, the GPS receiver 14may include a front end and a digitizer only. In this embodiment, otherGPS receiver components, the processor 16 and the memory 18 may behosted remotely on a server, for example.

As shown in FIG. 3, the GPS receiver 14 is capable of receiving signalsfrom GPS satellites and communicating with a non-GNSS positioningsoftware application 20. The non-GNSS positioning software application20 may be stored as computer readable code in memory 18 of the mobiledevice 10 or, alternatively, stored on a server remote from the mobiledevice 10. The non-GNSS positioning application 20 may be anypositioning application capable of providing a coarse position estimate.Example of non-GNSS positioning applications include: WiFi-basedpositioning, cellular-based positioning (including but not limited tomobile standards such as GSM, CDMA, UMTS, LTE), land-mobile radiosystems (including but not limited to VHF systems used in private orpublic safety applications), radio-broadcast positioning (including, butnot limited position based on radio broadcast transmission towers suchas FM or TV stations), or other data network infrastructure basedpositioning (including but not limited to IP routers, data modems orInternet protocols such as GeoIP).

Referring also to FIG. 4, the GPS receiver 14 includes a signalprocessing unit 22, which acquires satellites, and a navigation unit 24,which fixes the position of the GPS receiver 14. As shown, the GPSreceiver 14 communicates with a satellite acquisition application 26 anda position determining application 28. The satellite acquisitionapplication 26 and the position determining application 28 are softwareapplications that are stored as computer readable code in memory 18 andare executable by the processor 16. In general, the satelliteacquisition application 26 identifies “true” or “best” pseudoranges whenmultiple candidate pseudoranges are determined in order to acquire moreGPS satellites and the position determining application 28 reducespositioning uncertainty when satellite availability is limited. The GPSreceiver 14 of FIG. 4 is capable of fixing its position when four orfewer satellites are acquired by the signal processing unit 22.

Referring still to FIG. 4, the signal processing unit of the GPSreceiver 14 receives satellite signals from available GPS satellites andsends pre-processed digitized satellite signals (I, Q) to the satelliteacquisition application 26. The signal processing unit 22 determines andsends pseudoranges of acquired satellites to the navigation unit 24,which in turn sends the pseudoranges of acquired satellites to theposition determining application 28. The estimated location area fromthe non-GNSS positioning application 20 is received by both thesatellite acquisition application 26 and the position determiningapplication 28 in order to fix a position of the GPS receiver 14. In oneembodiment, the satellite signals and the estimated location area arereceived at generally the same time.

The satellite acquisition application 26 uses the estimated locationarea from the non-GNSS positioning application 20 to discriminatebetween multiple candidate peaks in order to determine which one is the“true” or “best” correlation peak. When the GPS receiver correlates thepre-processed satellite signal with its locally generated replicas, theGPS receiver: i) may not find any candidate correlation peaks in thesignal, ii) may find multiple candidate correlation peaks due to signalattenuation or multipath, or iii) may find one distinct candidatecorrelation peak. When one distinct candidate correlation peak isidentified, a pseudorange associated with that candidate correlationpeak is determined by the GPS receiver 14 to be an acquired satellite.

Referring to FIG. 5, correlation peaks are output from a correlator 30,or matched filter, which is part of the signal processing unit 22, ofthe GPS receiver 14. The inputs of the correlator 30 are the GPSpre-processed signals and its replicas locally generated in the GPSreceiver 14. The correlator 30 may be referred to a grid of correlatorsbecause the correlator 30 includes a predefined search space. In priorart (assisted) GPS receivers, no satellite may be acquired unless adistinct correlation peak is found.

In general, correlators 30 use the estimated location area from thenon-GNSS positioning application 20 to define a correlation searchspace, accelerate a search and reduce an area of uncertainty in order toextract a distinct correlation peak. When a distinct correlation peak isnot found, multiple candidate correlation peaks are considered by thesatellite acquisition application 26. When multiple candidatecorrelation peaks are identified for a particular GPS satellite,candidate pseudoranges that correspond to the multiple candidatecorrelation peaks are calculated. The estimated location area from thenon-GNSS positioning application 20 is used in combination withpseudoranges of GPS satellites that have been acquired (i.e. satellitesfor which a distinct correlation peak was found) to select the “true” or“best” pseudorange out of the candidate pseudoranges when a “true” or“best” pseudorange exists.

Referring to FIG. 6, the satellite acquisition application 26 identifiescandidate correlation peaks in the signal at 32. When no candidatecorrelation peaks are found, no GPS satellite may be acquired at 34.When one distinct correlation peak is found, then the GPS satellite isacquired at 36. When more than one candidate correlation peak is found,candidate correlation peaks are selected, at 38, and candidatepseudoranges are determined at 40. All of the candidate pseudoranges,which includes the pseudoranges of GPS satellites that have beenacquired, and the estimated location area from the non-GNSS positioningapplication 20 are used at 42 to: estimate the receiver's position usingan estimator, which is part of the satellite acquisition application 26,detect incorrect pseudoranges out of the candidate pseudoranges and thenre-estimate the receiver's position with the best pseudorange using theestimator. A statistical analysis is used for identifying the bestpseudorange among the candidates. The statistical analysis relies on theestimator's misclosure vector, which identifies the error between thecandidate pseudoranges and those estimated by the estimator, and apriori knowledge of the quality of the pseudoranges, which is a functionof received signal strength and satellite elevation and provides theinitial standard deviation of the pseudoranges. Based on the a prioriknowledge of the quality of pseudoranges and the misclosure vector, astatistical distribution is obtained. Candidate pseudoranges that do notfall into the statistical distribution are rejected, leaving behind thebest pseudorange. At 44, the position of the GPS receiver may be fixedusing the navigation unit 24 or the position determining application 28.

Referring to FIG. 7, in one example, four candidate correlation peaks ofa satellite vehicle (SV) are found and four candidate pseudoranges(c{circumflex over (ρ)}₁, c{circumflex over (ρ)}₂, c{circumflex over(ρ)}₃ and c{circumflex over (ρ)}₄) are calculated based on the candidatecorrelation peaks. The estimator then uses all of the candidatepseudoranges, which includes the pseudoranges of GPS satellites thathave been acquired, identified by reference numerals 46 and 48, and theestimated location area from the non-GNSS positioning application 20 toestimate the receiver's position. The estimated position will be biasedbecause of the presence of incorrect pseudoranges. Statistical analysisis then performed using the a priori knowledge of the pseudoranges andthe misclosure vector to identify the “true” or “best” pseudorange. Thenthe estimator uses the best pseudorange and the estimated location areafrom the non-GNSS positioning application 20 to estimate the receiver'sfinal position, which is the unbiased and best estimate. As shown inFIG. 7, the candidate pseudorange c{circumflex over (ρ)}₂ is identifiedas the best pseudorange. Thus, a third GPS satellite is considered to beacquired with a true pseudorange value, {circumflex over (ρ)}_(SV) _(#3), equal to c{circumflex over (ρ)}₂. As shown, the final two-dimensionalposition fix is estimated from the acquired GPS satellites and theposition uncertainty of the estimated location area from the non-GNSSpositioning application.

In general, the satellite acquisition application 26 increases thenumber of acquired GPS satellites and hence, improves overall satelliteavailability and satellite geometry. The satellite acquisitionapplication 26 has the ability to accept multiple candidate correlationpeaks, perform calculations therewith, and then use the estimatedlocation area from the non-GNSS positioning application 20 to recommendthe “true” or “best” correlation peak.

Referring back to FIG. 4, the position determining application 28 usesdifferent methods to find a fix for the position of the GPS receiver 14depending on the number of GPS satellites that are available. Referringalso to FIG. 8, when information from three GPS satellites is received,the position of the GPS receiver 14 is solved using the estimatedlocation area from the non-GNSS positioning application 20, receiverclock bias (t_(u)) and all of the pseudoranges, which may includedistinct as well as candidate pseudoranges. For example, two distinctcorrelation peaks of two satellites and multiple candidate correlationpeaks of the third satellite may be included.

Referring to FIG. 8, at 50, information from at least two satellites isreceived and pseudoranges are computed either by one or both of thesignal processing unit 22 and the satellite acquisition application 26.At 52, the receiver clock bias (t_(u)) is estimated from the GPSreceiver's previous position fix. The position determining application28 then computes the possible GPS receiver positions using candidatepseudoranges, which may include pseudoranges of acquired GPS satellites,the estimated location area from the non-GNSS positioning application 20and the receiver clock bias (t_(u)) at 54. The statistical outputs ofthe position determining application 28, such as the misclosure vector,are then used for detecting the incorrect pseudoranges using thestatistical analysis at 56, which may be referred to as a blunderdetection method. The blunder detection method generally uses thedifference between estimated pseudoranges determined at 54 and thecandidate pseudoranges corresponding to the non-acquired satellitesdetermined at 50. Candidate pseudoranges causing statistical blundersare identified by the blunder detection method at 56 and, at 58, thecandidate pseudoranges causing statistical blunders are removed leavingthe best pseudorange, which is then used for position estimation, at 54,in a subsequent iteration. When no blunders are detected at 56, themethod ends at 56.

In one example, when information from two GPS satellites 60, 62 isreceived as shown in FIG. 9A, the GPS receiver 14 is unable to estimateits position and hence executes the method of determining a location ofa GPS receiver 14 of FIG. 8. At 50, the GPS receiver 14 receivesinformation from two GPS satellites. In this example, two distinctcorrelation peaks are determined so that a single pseudorangecorresponding to each GPS satellite is determined. At 52, the receiverclock bias (t_(u)) is estimated from the GPS receiver's previousposition fix. The estimator of the position determining application 28then computes the possible GPS receiver positions using the pseudorangesof the GPS satellites that have been acquired, the estimated locationarea from the non-GNSS positioning application 20 and the receiver clockbias (t_(u)) at 54. At 56, the estimator's misclosure vector and apriori knowledge of the quality of the pseudoranges are used by theblunder detection method to identify incorrect candidate pseudoranges.Since no candidate pseudoranges were initially determined, no blundersare detected and the receiver position estimation ends at 56.

As shown in FIG. 9B, the estimated position 64 derived from the non-GNSSpositioning application 20 using, for example, Access Points (APs), isused by the estimator to estimate the receiver's position. An AP is awireless router or device that is used to access data networks. An APmay be WLAN router, 762.11 g, 762.11b or a cellular base station (i.e.GPRS, EDGE, 3G, 4G). As shown, the final position 66 estimates for theGPS receiver 14 are based on acquired GPS satellite information, 60 and62, as well as the estimated location area 64 from the non-GNSSpositioning application, (i.e. two-dimensional position variance).

FIG. 9C schematically depicts how a hybrid positioning system of theprior art determines a position of a GPS receiver. In this scenario, thehybrid positioning engine relies more on an estimated location area 70from the non-GNSS positioning application. This may occur when thepseudoranges have greater uncertainty (ie. large standard deviation)when compared to the estimated location area 70 from the non-GNSSpositioning application. The final position fix 68 is represented by({circumflex over (x)}, ŷ), while the shaded area around the fixedposition represents the positioning uncertainty retrieved from theestimated location area 78 from the non-GNSS positioning application.

An advantage to the method of determining a location of a GPS receiver14 is that the final position, as well as the position uncertainty, isbased on information from the acquired GPS satellites as well as theestimated location area from the non-GNSS positioning application. Assuch, the final position fix, and its uncertainty, is more accurate andreliable than prior art hybrid and non-GNSS positioning applicationswhere more weight was given to the location area from the non-GNSSpositioning application.

The GPS receiver 14 may operate using the satellite acquisitionapplication 26, the position determining application 28 or both thesatellite acquisition application 26 and the position determiningapplication 28. Referring to FIG. 10, the GPS receiver 14 uses thesatellite acquisition application 26 to acquire satellites, at 72, andthe position determining application 28 to fix a position of the GPSreceiver 14, at 74. Using the satellite acquisition application 26, twodifferent sets of pseudoranges are determined. The first set ofpseudoranges, [1, . . . , M], are derived from acquired GPS satelliteseach with a distinct correlation peak. The second set of pseudoranges,[1, . . . , N], are candidate pseudoranges derived from multiplecandidate correlation peaks for each GPS satellite pseudorange. Thesatellite acquisition application 26 determines the “true” or “best”pseudorange for the respective GPS satellites based on blunder detectionand the non-GNSS positioning application. When the “true” or “best”pseudoranges have been determined, the satellite pseudoranges areconsidered to be acquired and are then used in the position determiningapplication 28 of FIG. 4.

Referring to FIG. 11, another example of a GPS receiver 14 that usesboth the satellite acquisition application 26 and the positiondetermining application 28 to acquire satellites and fix a position ofthe GPS receiver 14 is shown. In this example, one GPS satellite hasbeen acquired by a stand-alone GPS receiver, as indicated by referencenumeral 76, and the stand-alone GPS receiver fails to fix its position.In order to acquire a second GPS satellite, two candidate correlationpeaks, which were found by the correlator 32, are used to calculate twocandidate pseudoranges, which are indicated by reference numerals 78 and80. The three candidate pseudoranges, which includes the pseudorange ofthe acquired GPS satellite, along with the estimated location area 82from a non-GNSS positioning application are used by the estimator toestimate the receiver's position. The blunder detection method thenidentifies the best pseudorange, which is used by the estimator to fixthe position 84 of the GPS receiver 14.

In one embodiment, a GPS receiver 14 is capable of switching betweenoperating as: i) a standalone GPS receiver, which receives signals fromfour GPS satellites, ii) an assisted-GPS receiver, which uses GNSSorbital data or estimated location areas from a non-GNSS positioningapplication to allow the GPS receiver to locate GPS satellites in rangemore quickly, iii) a GPS receiver operable when satellite availabilityis limited and iv) a GPS receiver 14 operable when more than onecorrelation peak is determined.

FIG. 12 depicts an example of collaboration between the GPS receiver 14,the satellite acquisition application 26, the position determiningapplication 28 and the non-GNSS positioning application 20. Thesatellite acquisition application 26 and the position determiningapplication 28 of the mobile device 10 may collaborate with otherrelated satellite acquisition applications 26 and position determiningapplications 28, operating on the same or different mobile devices. Ingeneral, GPS receivers in different devices may collaborate when the GPSreceivers are within an acceptable range of one another based onnon-GNSS positioning.

The signal processing unit 22 of the GPS receiver 14 performscorrelation and identifies the number of candidate correlation peaks. Asshown, the signal processing unit 22 uses a signal tracking application86 to convert the candidate correlation peaks to pseudoranges byestimating the propagation delay. At 88, when all of the pseudorangesare identified as unique and the total number of pseudoranges isdetermined, at 90, to be at least four then GPS position is fixed, at92, without using the location area estimate from the non-GNSSpositioning application 20. At 88, when the pseudoranges are not uniquedue to multiple candidate correlation peaks, the satellite acquisitionapplication 26 is used for identifying the best pseudorange using theblunder detection method 56. After blunder detection, the positiondetermining application 28 is used to estimate the receiver's position,which includes checking for at least two pseudoranges and either i)estimating the receiver's position using all of the pseudoranges as wellas the location area estimate from the non-GNSS positioning application,as indicated at 94, or, ii) reporting the non-GNSS position as a fallback, as indicated at 96.

The methods and apparatus of the present embodiments facilitate fixingof a three-dimensional position of a GNSS receiver, such as a GPSreceiver, when the number of acquired satellites is less than four orthe satellite geometry is far from optimal. By integrating GNSS andnon-GNSS positioning systems, rather than using a non-GNSS positioningsystem as a fallback, greater accuracy in position determination may beachieved. The methods and apparatus described herein provide 1) improveddiscrimination between possible pseudoranges so that more GPS satellitesmay be acquired as compared to stand-alone modes and 2) a reduction inthe area of positioning uncertainty.

The above-described embodiments are intended to be examples only.Alterations, modifications and variations can be effected to theparticular embodiments by those of skill in the art without departingfrom the scope of the present application, which is defined solely bythe claims appended hereto.

1. A method of determining a position of a GNSS receiver comprising:receiving, at the GNSS receiver, information from at least two GNSSsatellites; receiving, at the GNSS receiver, an estimated location areafrom a non-GNSS positioning application; determining candidatepseudoranges corresponding to candidate correlation peaks determinedbased on the information received from the at least two GNSS satellites;determining possible positions of the GNSS receiver using the candidatepseudoranges and the estimated location area; determining a bestpossible position of the GNSS receiver from the possible positions; andsetting the best possible position as the position of the GNSS receiver;wherein when multiple candidate correlation peaks corresponding to oneof the at least two GNSS satellites are determined, the estimatedlocation area is usable to reduce the number of candidate correlationpeaks prior to candidate pseudoranges being determined.
 2. A method asclaimed in claim 1, wherein determining a best possible position fromthe possible positions comprises: using a misclosure vector representingdifferences between the candidate pseudoranges and the possiblepositions and an indication of pseudorange quality.
 3. A method asclaimed in claim 1, wherein the indication of pseudorange quality isbased on received signal strength and satellite elevation of the GNSSsatellite associated with the pseudorange.
 4. A computer readable mediumcomprising instructions executable on a processor for implementing themethod of claim
 1. 5. A method as claimed in claim 1, wherein theinformation from at least two GNSS satellites and the estimated locationarea from the non-GNSS positioning application are received at generallythe same time.
 6. A method as claimed in claim 1, wherein the non-GNSSpositioning application is an application capable of providing aninitial position.
 7. A method as claimed in claim 5, wherein thenon-GNSS positioning application is based on one of: WiFi, Cellular,land-mobile radio, radio broadcast and GeoIP.
 8. A method as claimed inclaim 1, comprising receiving GNSS satellite information from a GNSSreceiver of another mobile device.
 9. A method as claimed in claim 1,wherein at least one of the candidate pseudoranges corresponds to anacquired one of the GNSS satellites.
 10. A mobile device comprising: anantenna; a GNSS receiver for receiving information from at least twoGNSS satellites and for receiving an estimated location area from anon-GNSS positioning application; and a processor in communication withthe GNSS receiver; the processor determining candidate pseudorangescorresponding to candidate correlation peaks determined based on theinformation received from the at least two GNSS satellites, determininga best possible position of the GNSS receiver from possible positions ofthe GNSS receiver determined using the candidate pseudoranges and theestimated location area and setting the best possible position as theposition of the GNSS receiver; wherein when multiple candidatecorrelation peaks corresponding to one of the at least two GNSSsatellites are determined, the estimated location area is usable toreduce the number of candidate correlation peaks prior to candidatepseudoranges being determined.
 11. A mobile device as claimed in claim10, wherein the processor receives GNSS satellite information from aGNSS receiver of another mobile device.
 12. A mobile device as claimedin claim 10, wherein at least one of the candidate pseudorangescorresponds to an acquired one of the GNSS satellites.